The present invention relates to an apparatus and method for controlling the heating of metal such as for pre-weld or post-weld heat treatment, stress relief, or for controlling the heating of metallic conduits and containers to prevent the freezing and improve the fluidity of materials contained therein. In more detail, the present invention relates to an apparatus which controls an applications power supply for heating a workpiece to a desired temperature at a desired rate without passing the power produced by that power supply through that apparatus as well as a method of controlling that power supply to achieve that same result.
The importance of heating metal before, during, and/or after welding is well documented. Preheating, a term used to describe heating both prior to and during welding, helps prevent the terminal strains set up during welding that can crack the weld, protects against the high thermal conductivity of, for instance, relatively thick carbon steel which causes heat loss from the welded area, increases the diffusion rate of crack-promoting hydrogen, facilitates removal of hydrogen from a welded joint, and drives off harmful moisture. Postheating, or post-weld heat treatment, relieves residual stresses in the weld due to the restraint by the parent metal during weld solidification to provide increased ductility in the weld metal and a decrease in hardness, improves corrosion resistance and resistance to caustic embrittlement, and improves machining stability. Recognition of the importance of heat treating throughout the metal-working and fabrication industry has given rise to a whole industry in which companies specializing in heat treatment render, for instance, on-site heat treating services on a contract basis during, for instance, the construction of bridges, refineries, nuclear reactors, and other structures which must be welded.
In spite of the availability of these contract services and the recognized importance of heat treatment, there remains a large number of welds that are not heated, pre- or post-weld, or which are not effectively heat treated, because of the cost of such treatment, a lack of necessary equipment, or because such treatment is deemed unnecessary because the metal joint has been "over-engineered", e.g., made of metals that are so much stronger/durable than is required by the particular application that they are strong enough to meet specifications even after they are weakened by the weld. It is to these latter wasteful efforts that the present invention is directed in that an apparatus and method are provided that are so relatively inexpensive to purchase and easy to operate that heat treatment is brought within the means and capabilities of any legitimate welder and/or fabricator.
Another goal of the present invention is to provide an apparatus for use in heat treatment that operates in conjunction with the equipment which is commonly used for welding and/or heat treating metals.
Another goal of the present invention is to provide a method of using the equipment which is commonly used for welding and/or heat treating metal.
Another goal of the present invention is to provide an apparatus and method by which the rate at which the metal is heated is controlled, again with commonly used welding equipment.
Another goal of the present invention is to provide an apparatus for heating metal which is light in weight and small, thereby facilitating the transport of the apparatus.
Another goal of the present invention is to provide an apparatus and method for use in conjunction with the equipment commonly used for welding and/or heat treating metals which controls the power output of such equipment at two selected power levels for pulsed operation.
Another goal of the present invention is to provide an apparatus and method for controlling the heating of metal to prevent freezing or improve the fluidity of materials contained within a metallic component such as a tank or pipeline.
A particularly important goal of the present invention is to provide a method and apparatus by which a metallic workpiece is heated to a desired temperature at a desired rate without passing the power used to heat the workpiece through the circuitry used for controlling the power supply, thereby increasing the safety of that equipment.
Other goals, and the advantages, of the present invention will be made clear by the following description of a presently preferred embodiment thereof.